This invention relates to a method of treating an insulating layer such as found in semiconductor devices.
As the designers of semiconductor architecture push the devices within the semiconductors closer and closer together, the permittivity of the insulating layers which are formed between the connecting metal tracks, becomes more significant. The trend is therefore to produce insulating materials with lower and lower dielectric constants (k). One approach to forming such materials is to introduce carbon into the insulating material and such a method is described in our co-pending International Patent Application PCT/GB97/02240, the disclosure of which is incorporated herein by reference.
In order to form the metal tracks separated by the insulating layer or to connect those tracks to other tracks or devices formed in the semiconductor material on which the insulating layers are deposited, it is necessary to etch into or through the insulating layer and subsequently fill those recesses with electrically conducting metal. Such recesses are generally formed by coating the upper surface of the insulating layer with a photo-resist, removing certain parts of the resist using photo-lithographic techniques, etching through the exposed openings in the resist to form the recesses and then removing the layer of resist by reactively etching the resist using oxygen.
However, it has been found that where the insulating layer contains carbon, the dielectric constant increases as a result of the reactive oxygen etching, the side walls of the formation are etched creating barrelling and there are subsequent problems with filling the recesses with metal.
From one aspect the invention consists in a method of treating an insulating layer in which a formation has been etched through a layer of resist comprising reactive etching the resist (for example with a plasma process), inhibiting the absorption or removing water vapour and/or oxygen at the exposed surfaces of the etch formation and filling the formation with conductive metal in the absence of said water vapour and/or oxygen.
The inhibiting step may include supplying hydrogen with or to an etchant gas, e.g. oxygen and/or it may comprise supplying nitrogen with or to the etchant gas. Preferably the step of inhibiting includes supplying a gas which is the source of reactive hydrogen and/or nitrogen with or to the etchant gas. In one embodiment the gas may be NH3. Where the etchant gas is oxygen, the ratio of oxygen to the gas may be approximately 3:1 and similar ratio""s may be appropriate with other etchant gases.
In an alternative arrangement the inhibiting step may be performed by maintaining the substrate under vacuum until the metallisation step is completed or there may be a removal step including heating the insulating layer prior to metallisation to outgas the insulating material.
Preferably the insulating layer has a dielectric constant of less than 4 and/or includes carbon. More particularly the dielectric constant is below 3.5 and most preferably below 3.0.
The carbon concentration in the dielectric film is most preferably more than 10%.
Although the invention has been defined above it is to be understood it includes any inventive combination of the steps set out above or in the following description.